Seems you made something wrong. But you don't provide enough info to spot your error. I can only say it works here.

What I did to install dev-util/idea:0. Synced portage and overlays1. Created a local overlay2. Downloaded the ebuild and patch-files from the fw-overlay3. Put them into appropriate places[3a. Optional: Renamed the ebuild to reflect the latest version - 13.1.2.135.690]4. Created manifest5. Emerged (without any errors)